1. Field of the Invention
The present invention relates to a pressure sensor for converting a fluid pressure into an electric signal to output to outside, which more specifically relates to an improvement in an assembly structure and signal-processing circuit board thereof.
2. Description of Related Art
In general, a pressure sensor for detecting a fluid pressure has a joint having a pressure port, a pressure detecting device attached to the joint for converting the fluid pressure introduced to the pressure port to an electric signal, a circuit board disposed immediately above the pressure detecting device and having a circuit for processing the electric signal from the pressure detecting device, and a housing for protecting the pressure detecting device and the circuit board (see, for instance, Japanese Patent Laid-Open Publication No. Hei 11-142267 and 11-237291).
FIG. 25 shows a structure of a conventional pressure sensor.
The pressure sensor has a joint 1 screwed to a mount A such as a tube shown in dotted line, a pressure detecting device 2 welded to the joint 1 and an output means 4 for outputting an electric signal toward outside in accordance with the pressure detected by the pressure detecting device 2.
The joint 1 is provided with a pressure port 13 for introducing fluid pressure at a center of a body 12 formed with a male thread 11 screwed to the mount A on an outer wall thereof, and a butt welding portion 15 widening in tapered manner projects upward from a surface of the joint 1 at the upper center of the joint 1. A flange 14 is integrally formed on an upper portion of the body 12, where a thin crimping part 1A is carved on an upper outer wall of the flange 14.
The pressure detecting device 2 is welded to the butt welding portion 15 and a metal case 1B is welded to an upper surface of the flange 14. A lower end of the housing 5 as a connector is fitted between the case 1B and the crimping part 1A through an O-ring 38 and is caulked by the crimping part 1A.
A cylindrical base 1D surrounding the pressure detecting device 2 is held by a projection 1C formed by bending a part of the case 1B. A support piece 1E is formed by cutting and raising an upper inside of the case 1B. A circuit board 7 connected to the pressure detecting device 2 is supported by the support piece 1E.
Since the body 12 and the flange 14 of the joint 1 are integrated in the conventional pressure sensor, following disadvantages occurred.
In order to weld the pressure detecting device 2 to the butt welding portion 15, the butt welding portion 15 has to be projected above the surface of the flange 14. It is because, when the butt welding portion 15 is retracted relative to the flange 14, the pressure detecting device 2 has to be welded from obliquely above in a narrow space, which makes welding management such as weld line alignment difficult. However, when the butt welding portion 15 is projected above the surface of the flange 14, the entire length of the pressure sensor and size thereof can be increased accordingly.
In order to restrain enlargement of the outer diameter of the pressure sensor, the circuit board 7 may preferably be located above the pressure detecting device 2. However, in the conventional arrangement, since the pressure detecting device 2 projects above the surface of the flange 14, the circuit board 7 has to be supported by the support piece 1E to be away from the pressure detecting device 2, thus lengthening the pressure sensor.
Further, since the crimping part 1A for fixing the housing 5 is carved to be a thin portion, much work is necessary for processing, thereby increasing production cost.
Elimination of the above disadvantage of the conventional pressure sensor has been strongly desired, where the entire length can be shortened, weld line alignment work can be facilitated and eliminating the need for machining work of the crimping part to reduce production cost.
On the other hand, in a pressure sensor according to the above-described Japanese Patent Laid-Open Publication No. Hei 11-142267 (first conventional art), since a hole for accommodating the pressure detecting device is formed at the center of the circuit board, a circuit component such as integrated circuit has to be located outside the circuit board, so that the outer diameter of the circuit board are increased, thereby making it difficult to reduce the size (diameter) of the product.
In a pressure sensor according to the above-described Japanese Patent Laid-Open Publication No. Hei 11-237291 (second conventional art), since the integrated circuit opposes the pressure detecting device and the pressure detecting device and the circuit board are connected through a spacer, the number of the component and assembly process is increased, thereby also making it difficult to reduce the size (height) of the product.
When a pressure sensor is disposed under an environment with much electromagnetic wave noise, an electric component weak in noise, such as an integrated circuit, has to be protected against foreign noise. When an electro-conductive lid member covering the electric component is separately provided in order to protect the electric component such as integrated circuit from the foreign noise, size reduction becomes difficult. Accordingly, a technique has been proposed where a ground-plane is provided to an intermediate layer of a multi-layered board to form a shielded space (Japanese Patent Laid-Open Publication No. 2000-214040).
Such multi-layered board may be applied to the circuit board of a pressure sensor as shown in, for instance, FIG. 26 and FIG. 27.
The pressure sensor shown in FIG. 26 has a joint 1, a pressure detecting device 2 welded to the joint 1, and a multi-layered circuit board 7 held on the joint 1 and having a ground-plane layer 71 thereinside. The circuit board 7 has an opening 72 for the pressure detecting device 2 to be accommodated at the center thereof. An input/output terminal 77 and a filter circuit 82 are respectively provided on the upper surface of the circuit board 7, and an integrated circuit 81 is mounted on the lower side thereof. The pressure detecting device 2 and the circuit board 7 are connected via a bonding wire 80.
The pressure sensor 27 shown in FIG. 27 has a joint 1, a pressure detecting device 2 welded to the joint 1, and a multi-layered circuit board 7 held on the joint 1 and immediately above the pressure detecting device 2, the circuit board 7 having a ground-plane layer 71 thereinside. The pressure detecting device 2 and the circuit board 7 are connected by a bonding wire 80 via a through-hole opening 72 formed on the circuit board 7.
Since the pressure sensor shown in FIG. 26 can accommodate the pressure detecting device 2 in the opening 72 of the circuit board 7, the height thereof can be reduced and the entire length of the pressure sensor can be shortened. On the other hand, since the diameter of the circuit board 7 in width diameter can be enlarged as in the first conventional art, thereby making it difficult to reduce the size of the pressure sensor.
In the pressure sensor having structure as shown in FIG. 27, since the circuit board 7 is located immediately above the pressure detecting device 2, the diameter of the circuit board 7 in width direction can be reduced and external diameter of the pressure sensor can be reduced. On the other hand, the height thereof is increased, thereby making it difficult to reduce size of the pressure sensor as in the second conventional art. Further, since the distance between the circuit board 7 and the pressure detecting device 2 is increased, the bonding wire 80 is lengthened, thereby deteriorating efficiency in bonding the wiring, and resonance frequency of the wiring is lowered to deteriorate anti-vibration properties thereof.
Accordingly, a pressure sensor having improved circuit board capable of reducing entire length and diameter, improving workability of wire-bonding and anti-vibration properties has been strongly desired.
An object of the present invention is to provide a pressure sensor capable of solving the above problems, reducing entire length thereof, facilitating weld line alignment, and eliminating the need for carving the crimping part to reduce production cost.
Accordingly, in the present invention, the joint, the flange member and the connector are separated and are bonded so that the pressure detecting device does not project from the flange member.
A pressure sensor according to the present invention has: a joint having a pressure port; a pressure detecting device attached to the joint for converting a fluid pressure introduced to the pressure port into an electric signal; a housing provided to an output side of the pressure detecting device; a flange member bonded to the joint and having a through-hole for accommodating the pressure detecting device at a center thereof; and a connector bonded to the flange member to fix the housing.
According to the above arrangement, since the joint and the flange member are separated and bonded subsequently, the flange member can be bonded after welding the pressure detecting device to the joint, so that butt welding can be used for pressure detecting device to an exposed part having no flange member, thereby facilitating weld line alignment etc.
Since the pressure detecting device can be arranged in a manner not to protrude relative to the upper surface of the flange member, the entire length of the pressure sensor can be reduced.
Further, since the connector is also arranged as an independent body, it is not necessary to carve a thin crimping part on the flange member, so that production cost can be reduced.
In the pressure sensor of the present invention, the connector may preferably have an outer wall on an outside of an inner wall with an annular groove therebetween. And the outer wall may be arranged as a crimping part, the lower peripheral end of the housing may preferably be fitted to the annular groove and the housing may preferably be caulked and fixed by the crimping part.
In the present invention, the connector may preferably have a substantially cylindrical inner wall, a substantially cylindrical outer wall coaxially disposed on an outside of the inner wall and an annular groove formed between the inner wall and the outer wall.
In the above arrangement, a crimping part formed at a peripheral end of the outer wall opposite to the flange member may preferably be provided, and the housing may preferably have a lower end fitted to the annular groove and be caulked by the crimping part.
According to the above arrangement, the connector can be easily and inexpensively produced by presswork of a metal material and the housing can be easily fixed only by deforming and crimping the outer wall of the connector. At this time, a sealing member (e.g. O-ring) may be interposed between the lower end of the housing and the outer wall or the inner wall.
The outer wall may extend on the entire circumference on the outside of the inner wall or, alternatively, may be partially provided at several locations on the outside of the inner wall.
In the pressure sensor of the present invention, either one of lug and notch being mutually fitted may preferably be formed on the inner wall and the housing.
By forming such fitting of the lug and notch, the rotation of the connector and the housing can be prevented, thereby enhancing work efficiency in assembly process.
In the above arrangement, a plurality of pairs of the lug and the notch may preferably be formed, one of the pairs having dimension or configuration different from the other pair.
Alternatively, a plurality of pairs of the lug and the notch may preferably be formed, the pairs being arranged along circumferential direction of the inner wall with unequal interval.
With the use of different lug and notch fitting, the rotary angle position between the connector and the housing can be uniquely determined, thereby smoothly and efficiently conducting assembly to a predetermined relative position.
In the pressure sensor of the present invention, a terminal base may preferably be located inside the housing, and a bent end capable of being bent toward inside may preferably be formed at a peripheral end of the inner wall opposite to the flange member, the bent end crimping and fixing the terminal base to the flange member.
According to the above arrangement, the terminal base can be easily fixed only by deforming and crimping the inner wall of the connector.
In the above arrangement, the peripheral end of the inner wall opposite to the flange member may preferably be divided by a plurality of notches.
Accordingly, crimping process can be easily conducted.
In the pressure sensor of the present invention, either one of lug and notch being mutually fitted may preferably be formed on the inner wall and the terminal base.
With the use of different lug and notch fitting, the rotation of the connector and the terminal base can be prevented, thereby enhancing work efficiency during assembly process.
In the above arrangement, a plurality of pairs of the lug and the notch may preferably be formed, one of the pairs having dimension or configuration different from the other pair.
Alternatively, a plurality of pairs of the lug and the notch may preferably be formed, the pairs being arranged along circumferential direction of the inner wall with unequal interval.
With the use of different lug and notch fitting, the rotary angle position between the connector and the terminal base can be uniquely determined, thereby smoothly and efficiently conducting assembly to a predetermined relative position.
In the pressure sensor of the present invention, a circuit board connected to the pressure detecting device may preferably be located on an upper side of the flange member.
In mounting the circuit board, the circuit board may preferably be fixed using adhesive etc.
According to the above arrangement, the entire length of the pressure sensor can be reduced by disposing the circuit board directly on the flange member. Further, since the circuit board is disposed directly on the flange member, the support base for supporting the circuit board above the pressure detecting device can be omitted, thereby reducing the number of components and production cost.
In the pressure sensor of the present invention, the circuit board may preferably include: a ground land capable of being soldered formed on the surface of the circuit board; and a ground terminal soldered to the ground land and welded to the flange member.
According to the above arrangement, the ground terminal can be soldered in mounting the component to the circuit board, so that the circuit board can be mounted to the pressure sensor only by welding to the flange member, thereby omitting repeated soldering process. Specifically, in the conventional arrangement, though the flux is removed after mounting the components on the circuit board, subsequent flux removal is necessary when the circuit board is installed to the pressure sensor in the subsequent process. By using the ground terminal of the present invention, only welding is necessary in mounting to the pressure sensor, so that repeated soldering and flux removal can be omitted, thereby simplifying production process.
Another object of the present invention is to improve the arrangement of the circuit board, thereby providing a pressure sensor capable of reducing entire length and diameter and improving workability of wire-bonding and vibration strength.
In the pressure sensor of the present invention, the circuit board may preferably have a multi-layered structure of a plurality of conductor layers, and at least one of the conductor layer may preferably have a projection projecting relative to the other conductor layer, the projection being located around immediately above the pressure detecting device.
According to the above arrangement, since the at least one of the conductor layer has the projection projecting relative to the other conductor layer and being disposed around immediately above the pressure detecting device, the conductor layer for the circuit component and connection can be provided on the projection, so that the component can be disposed without widening the circuit board and the size of the pressure sensor can be reduced. Further, the distance between the pressure detecting device and the conductor layer can be reduced, the bonding wire can be shortened, the work efficiency of wire bonding can be improved and vibration strength can be improved.
In the pressure sensor of the present invention, the circuit board may preferably have an opening for accommodating the pressure detecting device and the uppermost conductor layer may preferably be projected to the opening to form the projection.
According to the above arrangement, since the pressure detecting device is accommodated in the opening, the height can be reduced, thereby reducing entire length, i.e. the size, of the pressure sensor.
In the pressure sensor of the present invention, at least one of the conductor layers near the pressure detecting device may preferably project relative to the other conductor layer to form the projection, the conductor layer having the projection and the pressure detecting device may preferably be connected, the conductor layer other than the conductor layer having the projection may preferably be a ground-plane layer, and a circuit component for forming a circuit on the circuit board may preferably be provided on a surface of the circuit board facing the pressure detecting device.
Accordingly, since the bonding wire is connected from the projection near the pressure detecting device to the pressure detecting device, the wiring length can be shortened and the circuit component can be located in a shielded space formed by the ground-plane layer to provide protection against noise.
In the pressure sensor according to the present invention, a recess may preferably be formed on a pressure detecting device side of the circuit board, the circuit component forming a circuit being attached to the recess.
According to the above arrangement, since the circuit component is attached to the recess formed on the pressure detecting device side of the circuit board, the length of the bonding wire for electrically connecting the pressure detecting device and the circuit board can be further shortened. Further, by burying the circuit component in the recess, the circuit component can be located immediately above the pressure detecting device, the outer dimension of the circuit board can be further reduced. Accordingly, advantages such as the size reduction (height and diameter reduction) of the product and improvement in vibration strength and assembly efficiency can be obtained.
In the pressure sensor of the present invention, the circuit board may preferably be a multi-layered substrate using ceramics as an insulation layer.
According to the above arrangement, component mounting and ground connection are possible within a narrow space by the three-dimensional circuit board, so that the size of the pressure sensor can be reduced. Further, the heat resistance of the circuit board and noise immunity on account of high permittivity can be improved.